Magnetism, ions, and water: a Martian disappearing act
Magnetism, ions, and water: a Martian disappearing act lead image
A few million years after the formation of the solar system, the rocky planets cooled down, and some lost their global magnetic field. But Mars retained a crustal magnetic field, which redistributes plasma from solar winds through its southern ionosphere.
Using data from the Mars Atmosphere and Volatile EvolutioN (MAVEN) spacecraft, Man et al. studied the role of these crustal fields, finding them to be more complex than previously thought.
“A prevailing idea is that crustal magnetic fields can protect Mars’ atmosphere from escaping by shielding charged particles from moving outward into space,” said author Xioajun Xu. “Our study revealed for the first time that crustal fields can do much more.”
The researchers found the crustal magnetic fields serve as channels to transport charged particles from Mars’ dayside to its nightside. After the sun ionizes oxygen on the dayside, the magnetic fields move the ions to the nightside, where they collide and recombine, altering the atmospheric dynamics.
MAVEN orbits Mars to collect data on ion densities, crossing the crustal magnetic field as it moves from the southern nightside into the dayside from within the ionosphere. The researchers compared MAVEN data with ion velocity distributions to determine the ions’ sources and movements.
Mars’ magnetic dynamics have large implications, from offering insight on our sun — which has similar complex magnetism in its corona — to understanding where Mars’ water went for future habitability studies.
“Mars was once very wet, with abundant liquid water on its surface,” said Xu. “Scientists believe that the disappearance of Mars’ global magnetic field, due to the cessation of the core dynamo, led to significant atmospheric and water loss.”
Source: “Observations of the day-to-night transport of martian heavy ions by the closed crustal magnetic field across the terminator,” by Hengyan Man, Xiaojun Xu, Pu Yang, and Jun Cui, Physics of Fluids (2025). The article can be accessed at https://doi.org/10.1063/5.0265291 .
